Paul Karrer's long and distinguished career in chemistry included the study of sugars and plant pigments , subjects that led him to the description and synthesis of vitamin A as well as several other vitamins. Karrer's work with vitamins helped to solve their chemical riddle, enabling physiologists to define the way in which the body utilizes them. In 1937 Karrer shared the Nobel Prize for Chemistry for research that incorporated the vitamins A and B.
Paul Karrer was born in Moscow, Russia, on April 21, 1889, the son of Julie Lerch Karrer and Paul Karrer, a Swiss dentist who was practicing in Russia. At three years of age Karrer and his family returned to Switzerland, initially to Zürich, but later settling in the canton, of Aargau, a region in the north of the country. Karrer was educated in schools in this canton, and it was while in secondary school that he began showing a passion for science. In 1908 he entered the University of Zürich, ultimately studying chemistry under Alfred Werner, whose work on the linkage of atoms in molecules won him the Nobel Prize in 1913. Karrer, after completing his doctoral dissertation on cobalt complexes in 1911 and earning his Ph.D., became Werner's lecture assistant. His attention soon turned to organic arsenical compounds, and Karrer's first paper on the subject, published in 1912, caught the eye of Paul Ehrlich, a renowned chemist in Germany whose work at the turn of the twentieth century had helped to explain the action of poisons and how to neutralize their effects by antitoxins. Ehrlich subsequently invited Karrer to join him as a research assistant in Frankfurt-am-Main at the Georg Speyer-Haus, a research institute.
Karrer remained in Germany until the beginning of World War I when he was called back to Switzerland for national service. While serving in an artillery unit, he met and married Helene Frölich, the daughter of the director of a psychiatric clinic. They would have three sons, but only two of them, Jurg and Heinz, survived infancy. In 1915 Ehrlich died in Frankfurt, and Karrer accepted the position of researcher and director of the chemical research division of the Georg Speyer-Haus, returning to war-time Germany. Karrer stayed in Germany for the next three years, and during this time he focused more closely on plant product chemistry. Then in 1918 he returned to the University of Zürich, first taking a position as associate professor of organic chemistry, and with Werner's death in 1919, becoming a full professor of chemistry as well as director of the Chemical Institute. Karrer would remain at the University of Zürich for the rest of his career, acting as rector from 1950 to 1953.
Karrer, of necessity, had to split his time between administration, teaching, and research. With the latter, he turned his attention to the spatial or steric configuration of atoms in molecules of amino acids, proteins, and peptides. But by the late-1920s he had shifted his focus to the pigmentation of plants , and more specifically, to the anthocyanins, the blue and red colors of berries and flowers. Though these substances had been isolated by another researcher, Karrer--by splitting their macromolecules with enzymes--helped to clearly describe their chemical make-up. More importantly, it was these researches in plant pigments that eventually led him to his work on carotene.
From anthocyanin, Karrer moved on to crocin, the yellow pigment of flowers such as the crocus. In connection with yellow pigments, Karrer tackled the structure of carotenoids, the orange-to-yellow pigments found in foods such as carrots and sweet potatoes.Richard Kuhn, a German chemist, had managed to isolate beta-carotene at about this time, and he and Karrer became something of rivals in explaining beta-carotene's chemical constitution. By 1930 Karrer had solved the structure of the carotene molecule. It was a logical progression from the study of plant pigments to that of vitamins, for Karrer learned that the body actually synthesizes vitamin A from carotene. Thus, he was soon on the track of the chemical make-up of vitamins themselves. By 1931 Karrer had become the first scientist to describe the structure of a vitamin, successfully demonstrating that vitamin A is very similar to one half of the symmetrical carotene molecule. Up until the time of his discovery, scientists had thought vitamins to be some peculiar state of matter, perhaps a colloid--a dispersed solution in suspension. But Karrer managed to show that vitamin A, in specific, is made up of atoms of hydrogen, carbon, and oxygen in a regular ring-like formation.
Karrer carried on his vitamin research over the next decade, ultimately synthesizing vitamin A in the laboratory. He then went on to research the chemical structure of several B vitamins, riboflavin being the first that he actually synthesized. In 1937, for his work on carotenoids and flavins, he shared the Nobel Prize for Chemistry with Walter Haworth, an Englishman who researched the make-up of carbohydrates and vitamin C. Karrer, however, was not one to rest on his laurels, and the very next year he synthesized vitamin E, and soon after, vitamin K.
From vitamin research, Karrer turned to an investigation of the enzyme nicotinamide adenine dinucleotide (NAD) which is involved with the energy system of cells. By 1942 he had contributed greatly to the understanding of both the NAD structure and function in cellular electron transfer. In his sixties, Karrer went back to earlier work, both in carotenes and in poisons--this time alkaloids. In the former, he successfully synthesized all the carotenoids, some forty different compounds. His work in alkaloids helped to determine the structure of curare, a resinous extract from certain South American trees used by indigenous peoples for poison arrows. Its medicinal uses include general anesthesia and reduction of muscle spasms.
Apart from his research, Karrer was a tireless administrator and teacher, directing over 200 dissertations in his academic career. He was also a prolific writer, with over 1,000 publications to his credit, including the 1928 organic chemistry textbook, Lehrbuch der organischen Chemie. Aside from the Nobel, Karrer won numerous awards and prizes, among them the Marcel Benoist Prize from Switzerland in 1923, the Cannizzaro Prize from Italy in 1935, and the Officier de la Legion d'Honneur from France in 1954. Despite fame, wealth, and offers from universities around the world, Karrer stayed on in Zürich until his retirement in 1959, eschewing luxuries such as a car. He died on June 18, 1971, after a short illness.
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